Apparatus subjected to heat and cold alternately



Patented May 23, 1939 I UNITED "STATES,

I PATENT OFFICE aliens I APPARATUS SUBJECTED TO HEAT AND COLD ALTERNATELY Russell Franks, NiagaraFalls, N. Y., assignor to Union Carbide and Carbon Corporation, a corporation of New York No Drawing. Original application June 18, 1935, Serial No. 27,161. Divided and this application April 27, 1937, Serial No. 139,258

and tungsten greatly improve the impact 2' Claims.

The invention relates to apparatus and parts thereof which during use are alternately heated to temperatures above about 200 C. and cooled to temperatures in the neighborhood of C. or

5 lower, and it is the principal object of the invention to provide alloy steel apparatus and parts which under such conditions of use retain toughness and resistance to impact. This application is a division of my application Serial No. 27,161

filed June 18, 1935.

Numerous manufacturing processes, notably oil refining, employ pressure jvessels and machine elements at elevated temperatures, and not uncommonly this apparatus is subjected from time to time to zero or subzero temperatures, either by intentional refrigeration or by cold weather. Apparatus for use at high temperatures, particularly'in the presence of corrosive conditions, is frequently constructed from steel containing substantial amounts of chromium. Except in situations wherein the corrosive conditions are unusually severe, ferritic steel containing about 4% to 10% chromium is usually chosen as the most economical material. A small amount of molyb- 5 denum or tungsten is sometimes added to increase the strength and toughness of this steel at elevated temperatures.

It has been observed that the above described steel, after prolonged exposure to high temperatures, tends to lose a great-part of its resistance to impact at low temperatures, and equipment subjected alternately to very high and very low temperatures has frequently failed by cracking. Steel containing molybdenum or tungsten appears to be almost as susceptible to this type of failures as the steel containing no molybdenum or tungsten. x

Another difnculty encountered in the fabrication and use. of this steel is its ability to harden 4 and become brittle when rapidly cooled from high temperatures. This property increases con siderably the difllculties in designing, fabricating, and operating corrosion resisting equipment.

. The addition of suitable amounts of titanium 5 or columbium, or both, decreases theair-hardening ability of the ferritic chromium steels, and with a proper choice of composition the material may be made substantially non-hardenable by heat treatment. But the addition of these elem ments, alone, does noteliminate the above discussed loss of impact strength at subzero temperatures.

I have discovered that properly proportioned additions of 'columbium, together with molybdenum, tungsten, or mixtures of molybdenum strengths of ferritic chromium steels at subzero temperatures after prolonged holding at elevated temperatures. Incidental, but by no means inconsequential,.benefits imparted by these additions include a decrease in air-hardenability and an increase in resistance to corrosion and hightemperature oxidation.

Table A presents representative results of comparative tests which comprised holding wrought Table A Analysis I Izod Percent Percent Percent Percent Impact Cr 0 Mo Cb $87 0. 00 None None 33 5. 95 10 0. None 46 6. 41 06 None 0. 75 61 Results which are similar, although showing less marked differences, have been obtained in tests alternately at about 300 C. and about 0 C.

Table B shows the results of comparative tests wherein wrought steel samples were heated at about 900 C. for ten minutes, cooled in the air, and tested at room temperatures.

Table B Analysis Izod Brinell impact hard- Percent Percent Percent Percent ncss Cr 0 Mo Cb FLlbs. 6.87 0.06 None None 29 302 5.95 .10 0.65 None 23 340 6.41 .06 None 0.75 119 131 0.45 .00 0.50 .65 112 112 For the purposes of comparison with Tables A and B, Table C sets forth the properties of the steels in question, at room temperature, after annealing at 750 C. for four hours and air-cooling (heat treatment 8) and after annealing, subsequent holding at 475 C. for one month, and then air-cooling (heat treatment L).

The data in Tables A, B, and C are self-explanatory and indicate the improvements provided by the present invention. 7

, The invention comprises apparatus and parts thereof which during use are alternately heated to temperatures upwards of about 200 C. and cooled to temperatures substantially at or below about 0 0., and which consist of a ferritic alloy steel containing about 4% to 10% chromium; carbon in amounts not over'0.15%; about 0.25% to 1.5% tungsten, molybdenum, or mixtures thereof; columbium in an amount between 6 and 16 times the carbon content; not over about 0.75% silicon; the usual fractional percentages of manganese required in steel making practice; and the remainder substantially all iron. In making steels commercially, the lowest practical percentage of carbon is in the neighborhood of 0.01%.. Therefore, in the steels of the'present invention, 'the lowest practical percentage of columbium is about 0.06%.

The most extensive use of the invention will probably be in the form of tubes for use'in handling hot fluids, for instance in the pyrolysis of hydrocarbons, where the temperature durin periods of heating will be upwards of 400 C.

I claim:

1. Apparatus and parts thereof which during use are alternately heated to temperatures upwards of about 400 (3., cooled to temperatures at or below about 0 C. and subjected to impact stresses at the lower temperatures and which consists of a ferritic alloy steel containing about 4% to 10% chromium; 0.01% to 0.15% carbon; silicon in amounts not over about 0.75%; about 0.25% to 1.5% molybdenum; 0.06% to 2.4% columbium, the columbium content being 6 to 16 times the carbon content; the remainder substantially all iron.

2. Apparatus and parts thereof which durin use are alternately heated to temperatures upwards of about 200 0., cooled to temperatures at or below about 0 C. and subjected to impact stresses at the lower temperatures and which consists of a territic alloy steel containing about 4% to 10% chromium; 0.01% to 0.15% carbon; silicon in amounts not over about 0.75%; about 0.25% to 1.5% molybdenum; 0.06% to 2.4% columbium, the columbium content being 6 to 16 times the carbon content; the remainder substantially all iron.

, RUSSELL FRANKS. 

